Production of photographic emulsions



Patented Feb.14,1939 I 2,146,938

PRODUCTION OF PHOTOGRAPHIO EMULSIQNS Bruno Claus, Halle-on-the-Saale,

No Drawing. Application March 18, 1936, Serial No. 69,520. In GermanyApril 5, 1935 8 Claims. (01. 95-

My invention relates to photographic emulsions bromide of a, finer grainpreformed in the form and o e especially t means whereby emulsions of asediment and which may or may not have possessing particularly favorableproperties can been emulsified in an emulsion substratum such beproduced in a particularly simple and effective as for instancegelatine, the mixture thus obmanner. V tained being subjected to asuitable aging tem- As is well known to those skilled in the art,perature under the action of chemical substances the Production ofPhotographic emulsions by first favoring the aging process, such as forinstance causing the silver halide and more especially silsolutions ofammonia. ver bromide to be preformed separately and to In the carryingout of the new process, I may settle as a sediment and to thereafteremulsifyfor instance proceed as follows:-- 4 10 mg the silver salt in abinder such as for instance Eaample 1 gelatine, offers the advantage, ascompared with o other modes of preparation of such emulsions, A 10%solution of potassium bromide containthat it avoids the circumstantial,unreliable and me a ut 4% p tas u iodide d w i-may time-consumingsubsequent. washing, whereby further contain some. gelatine is mixedWith a 15 the preparation of photographic mixtures of 11- solution ofnitrate of silver, which solution may ver halides and gelatine or thelike are greatly also contain some gelatine, the two solutionsbesimplified. Hitherto this mode of proceeding 8 mixed in Such pr p thatin the merely allowed producing fine-grained phototure a ht excess ofbromide, for instance graphic emulsions, which were little sensitive toamounting to is Present The Silver hallde the action of light and toproduce similar emulformed in the solution is allowed to settle downsions, which are known under the name of as a Sediment, whi h i w WashedA P peptisation emul i it v di r. or .oflthis sediment, say one lfifthis then emulsified coarse grain size appeared impossible, in an aqueousgelatine solution contalmng am- I have now found that the solution ofthis monia (about 3% gelatine and 2% ammonia) r problem is of paramountimportance since my and the mixture 15 HOW heated p to 50 t0 experimentshav shown th t pepfisation emu]- varying in accordance with the degreeof sensisions of the kind aforesaid and more particularly tivity of thegelatine used- To the shghtly heated such emulsions of this kind whichhave been mixture is 110w gradually added some of the caused t age byadding ammonia, are not only washed silver halide sediment. and, ifnecessary, 30

to distinguished by t simplicity, t n t there 18 also gradually addedsome ammonia be produced but also by their high Sensi such an extentthatthe ammonia which evaptivlty to the action or light, which as a rulesurorates during P' period is replaced. to passes the sensitivity ofemulsions of the same stantially maintain the initial concentration,unorder of grain size which were produced accordtn the remainder of thesflver halide is i mg to some customary mode of production Now gelatineis added the mixture of silver 0 AS I have already mentioned above t washalide and gelatine until the emulsion contains hitherto om sslble tomduce 'tisation suflicientgelatine (about 9%). After the missemulsionsfi f a fine and apssnsitivity ing gelatine has thus been added, theemulsion a till be kept some time at an elevated temup to about 14 Din.According to the present may 8 inventionnowx am enabledtopmducepeptisafion perature without adding ammonia, and then the 40 ammoniastill present in the emulsion is cautious- 3:5 2;; g gf figfi g ggg :gz'i gg g g f ly neutralized, for instance by adding citric acid.

tivity to light, being in certain cases finer grained The emulsion nowready for pourmg" than corresponding emulsions of similar sensi- Example3 I i 45 "uvity which were fimduced according to A 10% potassium bromidesolution containing about 0.4% potassium iodide and which may also v Thenew process for. the production of peptisacontain a small proportion ofelatine, is mixed tion emulsions possessing these desirable DI D- with asolution of nitrate of silver, which may erties Substantially -fitherein, that to 8 also contain some gelatine." The silver halide 50silver halide e u more especially to a Silver formed in the mixture isallowed to settle as a b d Sediment which y. y "not yet sediment, whichis washed out and emulsified in have been emulsified in a binder, forinstance an aqueous 3% solution of gelatine, for instance gelatine, isgradually added during the aging by adding some ammonia. The emulsion isnow perloda silver halide and more silver divided; to one or the twoportions is added some proceeding is continued until the whole of theemulsion has been added. 'I now add so much gelatine, that the emulsioncontains about 9% gelatine. The mixture may be kept at an elevatedtemperature for some time without adding ammonia, until the greater partof the ammonia still present in the gelatine has evaporated; Theremaining emulsion may be neutralized by adding citric acid and may thenbe poured.

Example 3 300 grams silver nitrate are dissolved in 3000 ccms. distilledwater.- n the other hand, 210 grams potassium bromide, 7.5 gramspotassium iodide and grams gelatine are dissolved in another 3 litresdistilled water. The silver salt solution is now entered undercontinuous stirring in the alkali halide solution. After the silverhalide has formed and settled down as a sediment, the supernatant liquidis removed by decantation and the silver'bromide is washed once withdistilled water and divided in two parts. The first part is added undercontinuous stirring to a solution containing 400 grams gelatine and 100ccms. of a 25% ammonia solution in 4500 ccms. distilled water. Thismixture is kept minutes at 50 C. and there is now added to it the otherhalf of the silver halide-sediment together with another 100 ccms.-of aammonia solution. The mixture is kept further minutes at 50 C. undercontinuous stirring and the ammonia still present therein is neutralizedwith citric acid, until the emulsion shows only a very slight alkalineor a od remain unchanged. This general idea consists therein, that whilethe emulsion is being prepared, and more especially while it is beingdiadding to the em ulsions containing'substancessuch as ammonia, whichfurther the aging progested, there is slowly fed to the growing silverhalide grain fresh, if possible chemically pure silver halide. This canhe realized by gradually cess, during this process further quantities ofwashed-out silver halide having a finer grain and eventually of furthersubstances which further the aging process, such as ammonia. Inthisprocess the finer grained silver bromide'is dissolved by the ammoniapresent in the emulsion and now recrystallizes on the larger grains ofsilver halide already present in the emulsion, whereby the size of thesegrains is gradually increased.

By proceeding in the manner described, I am enabled to preparepeptisation emulsions of a relatively high order of grain size which aremore sensitive to the action of light than the emulsions of ,a similarorder of grain size produced according to customary methods, and furtherto simplify considerably the manufacture.

' substances Various changes may be made in the details disclosed in theforegoing specification without departing from the invention orsacrificing the advantages thereof.

'1. The method of aging photographic peptisation emulsions whichcomprises mixing sedimented silver halide, which has been freed fromadhering substances and emulsified in a liquid binder, with anotherportion of sedimented silver halide also freed from adhering substances,which has a finer grain than the aforesaid emulsified silver halide andcausing the mixture to get at a suitable temperature in the presence ofa substance adapted to promote the aging process.

2. The method of aging photographic peptisation emulsions whichcomprises mixing sedimented silver halide, which has been freed fromadhering substances and emulsified in a liquid binder, with anotherportion of sedimented silver halide also freed from adhering substancesand emulsified in a liquid binder which portion has a finer grain thanthe aforesaid emulsified silver halide and causing the mixture to age ata suitable temperature'in the presence of a substance adapted to promotethe aging process.

3. The method of aging photographic peptisa: tion emulsions whichcomprises mixing sedimented silver halide, which has been freed fromadhering substances and emulsified in a liquid binder and aged therein,with another portion of sedimented silver halide also freed fromadhering substances, which has a finer grain than the aforesaidemulsified silver halide and causing the mixture to age at a suitabletemperature in the presence of a substance adapted to promote the agingprocess.

4. The method of aging photographic peptisation emulsions whichcomprises mixing sedimented silver halide, which has been freed fromadhering substances and emulsified in a liquid binder and aged therein,with another portion of sedimented silver halide also freed fromadhering and emulsified in a'liquid binder which portion has a finergrain than the aforesaid emulsified silver halide and causing themixture to age at a'suitable temperature in the presence of a substanceadapted to promote the aging process.

5. The method of aging photographic peptisation emulsions whichcomprises mixing .sedimented silver halide, which has been freed fromadhering substances and emulsified in a liquid binder, with anotherportion of sedimented silver halide also freed from adhering substances,which 35 has a finer grain than the aforesaid emulsified silver halideand causing the mixture to age at a suitable temperature in the presenceof ammonia.

6. The method of aging photographic peptisation emulsions whichcomprises mixing sedimented silver halide, which has been freed fromadhering substances and emulsified in a liquid binder, with anotherportion of sedimented silver halide also freed from adhering substances,and emulsified in a liquid binder which portion has a finer grain thanthe aforesaid emulsified silver halide and causing the mixture to age ata suitable temperature in the presence of ammonia.

7. The method of aging photographic peptisation emulsions whichcomprises slowly and gradually mixing sedimented silver halide, whichhas been freed from adhering substances and emulsified in a liquidbinder, with another portion of sedimented silver halide also freed fromadhersubstances, which has a finer grain than the aforesaid emulsifiedsilver halide and causing the mixture .toiage at a suitable temperaturein the presence of a substance adapted to promote the aging process.

8. The method of aging photographic peptlsation emulsions whichcomprises slowly and gradually mixing sedimented silver halide, whichhas been freed from adhering substances and emulsifled in a liquidbinder, with another portion of

